Carcinogenesis, Vol. 20, No. 9, 1787-1792,
September 1999
© 1999 Oxford University Press
Carcinogenesis |
Molecular dosimetry of endogenous and ethylene oxide-induced N7-(2-hydroxyethyl) guanine formation in tissues of rodents
1 Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, NC 27599 and
2 Wadsworth Center for Laboratory and Research, New York State Department of Health, Empire State Plaza, PO Box 509, Albany, NY 12201, USA
The formation of N7-(2-hydroxyethyl)guanine (7-HEG) in DNA was investigated previously in target and non-target tissues of F-344 rats and B6C3F1 mice exposed to 
ISOdia10 p.p.m. concentrations of ethylene oxide (EO) using fluorescence-linked high-performance liquid chromatography [V.E.Walker et al. (1992) Cancer Res., 52, 4238–4334]. In order to study the dose–responses for 7-HEG at lower exposures, a highly sensitive and specific gas chromatography coupled with high-resolution mass spectrometry (GC–HRMS) assay was developed. DNA was extracted from liver, brain, lung and spleen of B6C3F1 mice and F-344 rats exposed to 0, 3, 10, 33 or 100 p.p.m. EO for 4 weeks (6 h/day, 5 days/week). Analysis of DNA from control rodents showed that endogenous 7-HEG varied from 0.2 ± 0.1 to 0.3 ± 0.2 pmol/µmol guanine in tissues of rats and mice. 7-HEG exhibited tissue- and species-specific dose–response relationships in EO-exposed animals. Linear dose–response relationships were evident in mouse liver, brain and spleen at exposures between 3 and 100 p.p.m.. Mouse lung exhibited a slightly sublinear response between 33 and 100 p.p.m. EO. The relationships were linear in liver and spleen of rats between 3 and 100 p.p.m. EO, but were slightly sublinear in brain and lung between 33 and 100 p.p.m. EO. The number of 7-HEG adducts present in rats exposed to 3 p.p.m. EO was 5.3–12.5 times higher than endogenous 7-HEG in unexposed controls. In contrast, mice exposed to 3 p.p.m. EO only had 1.3- to 2.5-fold greater numbers of 7-HEG adducts. The factors driving the exposure–response relationships are also likely to affect carcinogenic and mutagenic responses of rodents to EO. Likewise, a better understanding of the relationships between 7-HEG derived from low exposures to EO and endogenously formed 7-HEG may be important for the accurate extrapolation of risk to humans.
Abbreviations: 7-HEG, N7-(hydroxyethyl)guanine; EO, ethylene oxide; FD, fluorescence detection; GC–HRMS, gas chromatography coupled with high-resolution mass spectrometry; HPLC, high-performance liquid chromatography; PFBBr, pentafluorobenzyl bromide; SCE, sister chromatid exchange; TLC, thin-layer chromatography.
3 Present address: Department of Occupational Safety and Health, China Medical College, No. 91 Hsuesh Shih Road, Taichung, Taiwan
4 To whom correspondence should be addressed Email: james_swenberg{at}unc.edu
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